n. whatever happens to be available especially when offered to an unexpected guest or when brought by guests and shared by all

Etymologies

Spelled pot-luck before the 20th century, from pot +‎ luck. The sense “meal offered by a host to an unexpected guest” dates to 1592; into the early 20th century, the word was used only to mean “meal provided by the host”.[2][3][4] (Wiktionary)

Examples

Later on inauguration day, Nixon was hosting what he described as a potluck dinner for the public.

Conversation subsequent to the potluck held by our food activist group about a month ago: - Foodie 1: That lentil and onion dip was excellent.Foodie 2: Thanks. I like the recipe too.Foodie 1: It went so well with the bread.Foodie 2: Yeah, funny that. Amazing what you can find in a dumpster.Foodie 1: What? You got the bread from a dumpster?!Foodie 2: Would have gone to waste otherwise.Foodie 1: And brought it along here?! Foodie 2: Why not?Foodie 1: I feel violated.